Almost all the UK's most endangered butterfly species are continuing to decline, government advisers say.

Could vanish altogether

They add that a quarter of all resident species have declined by more than 50%, and plans to protect high-priority butterflies are not working.

The main problem for most butterflies is habitat loss, driven by intensified farming and forestry. The advisers say butterflies could vanish altogether if the decline continues.

A report, The State of Britain's Butterflies, details the insects' plight. It is published by the Joint Nature Conservation Committee (JNCC), which advises the government on national and international issues, together with the Centre for Ecology and Hydrology and Butterfly Conservation.

New evidence

The report is published in conjunction with the Millennium Atlas of Butterflies in Britain and Ireland. What it provides, JNCC says, is "conclusive new evidence that all our native butterfly species are suffering from a major loss of habitat, and that current protection measures have not been successful in halting the decline".

In the past 200 years five species have become extinct

The report says: "During the last 200 years, over half of our 59 resident species have undergone substantial loss of range, of more than 20%, including 15 that have declined by more than 50% and five that have become extinct.

"Many habitat specialist species have continued to decline in range rapidly over the last two decades, and data show that some species have undergone declines in abundance even on protected sites.

"Some species that are more widely distributed in the landscape have also declined in abundance, although their ranges may not have decreased overall. Habitat destruction, changing management and increasing fragmentation are the causes of most declines. These factors have been driven by the intensification of agriculture and forestry.

"Reform of the European Union's Common Agricultural Policy (CAP) and other land-use policies will be necessary to reverse declines."

Extremely sensitive

The JNCC's head of species advice, Dr Ian McLean, said: "Butterflies are extremely sensitive to the environment on which they depend, therefore they act as excellent indicators of the health of the countryside.

"While some butterflies have extended their range northwards due to the effects of climate change, it is clear that there is an overall downward trend in UK butterflies. Existing measures to try to conserve key species are not effective enough. "

JNCC and Butterfly Conservation are calling for more determined conservation efforts to address the causes of butterfly declines, including the reform of the existing CAP.

"If we don't take action now to halt the present rate of decline, butterflies flying across a summer meadow may become a thing of the past."

The report says climate appears to be the main factor causing butterflies to extend their range, with UK average spring and summer temperatures up by 1.5 and 1 degree Celsius respectively in the last 25 years.

Huge losses

The UK Government's Biodiversity Action Plan gives priority status to 11 butterfly species. In the last 20 years seven of these have continued their long-term declines, two have shown small recoveries, and one has been reintroduced after becoming extinct in the UK.

Dr McLean told BBC News Online: "What the report does is to spell out very clearly the extent of the problem confronting British butterflies.

"The losses already are huge. We now have just 2% of the flower-rich meadows we used to enjoy, and the monocultures that have replaced them are not butterfly-friendly.

"So over much of the UK a butterfly in a summer meadow is already a rare sight."